Olefin pyrolysis initiators



United States Patent Office 3,317,626 Patented May 2, 1967 of Ohio NoDrawing. Filed Feb. 19, 1964, Ser. No 345,863

20 Claims. (Cl. 260-680) This invention relates generally to thecracking of olefins. More specifically it relates to a method ofimproving the etficiency of olefin pyrolysis by use of initiators. Mostspecifically it relates to methods of improving the efficiency ofcracking of certain specific olefins to form specific diolefinsemploying olefin pyrolysis initiators.

It is known that most olefins may be thermally decomposed or cracked bysubjecting them to relatively high temperatures. By the terms cracking,decomposing," cracked," decomposed, pyrolysis and pyrolyzing and thelike, as employed throughout this application and the claims appendedthereto, is meant that the olefin molecule splits into two fragmentsfrom the appilication of heat. (This true thermal pyrolysis process isto be distinguished from dehydrogenation processes which re quire theeffect of a surface catalyst as Well as greater temperatures to removehydrogen efficiently from molecules to form more unsaturated molecules.)These fragments themselves become molecules of other lower molecularweight materials which will contain both carbon and hydrogen atoms. Thiswill be explained later in greater detail. Usually the thermaldecomposition or cracking of olefins is conducted in a closed zone orreactor at temperatures usually ranging from about 300 C. to about 1000C. This pyrolysis is usually conducted in the absence of oxygen. Olefinsnormally are cracked while they are in a gaseous state and may becracked either relatively pure or as mixtures with other hydrocarbons,usually in mixture with a saturated hydrocarbon, i.e., a mixed feedstream of pentene and pentane or they may be in mixture with diluentssuch as nitrogen, steam and the like.

As indicated, the cracking of olefins usually results in the formationof two lower molecular weight materials, each of which contain bothcarbon and hydrogen atoms. The particular lower molecular weightmaterials formed when olefins are pyrolyzed depends largely upon theconfiguration of the olefin subjected to the cracking proc ess. By theterm configuration as used throughout this application and claims, ismeant the position or location of the double bonds and the position orlocation and type of the side groups, if any, of the olefin in question.To explain this in more detail, an olefin containing 6 carbon atoms witha side methyl group attached to the second carbon atom of the main orstraight chain portion and the double bond in the 2 position, such amaterial is Z-rnethyl pentene-2, when subjected to cracking, will upondecomposition, produce as the predominant product the diolefin, isopreneor 2-methyl butadiene-l,3. and a lower molecular weight parafiin,methane. On the other hand, a 6 carbon olefin having a methyl groupattached to the second carbon atoms of the straight chain and the doublebond in the l posiiton, such a compound is Z-methyl pentene-l, whencracked, will produce as the predominant products two other lowermolecular weight olefins, isobutylene and ethylene. Therefore, theconfiguration of the particular olefin employed usually designates themain or predominant products which result from the cracking of theolefin. These differences in product obtained upon cracking of olefinicisomers are due to the fact that olefins crack at the carbon-to-carbonsingle bond in the position beta to the double bond, that is, thescission of the olefin occurs at the bond that is in a position beta tothe double bond or that the split in the olefin occurs between thecarbon atom next to the carbon which has the double bond attached to itand the carbon atom adjacent thereto. Thus, to sum up, if olefins are tocrack at all by the application of heat, they must contain in theirmake-up a carbon-to-carbon single bond which is in a position beta tothe double bond. Therefore, wherever the terms cracking of olefins,"olefins cracked," decomposition or decomposed and the like are employedin this application, is meant olefins which will crack upon theapplication of heat to form two lower molecular weight olefins or onelower molecular weight diolefin and a saturated hydrocarbon at the bondbeta to the double bond.

Employing the most favorable conditions conducive to cracking ofolefins, by application of heat alone, to form lower molecular weightmaterials, it has been found that olefins decompose at a low rate perpass through the cracking zone. The conditions found conducive to thecracking of olefins are the temperature in the cracking zone, theresidence time in the zone and the ratio of the olefin to the diluent,if any, employed. It is usually the practice, to effect an increase inthe overall yield of such a process, to separate the unreacted orundecomposed olefin from the products resulting from the decomposedportion of the olefin and return or recycle the unreacted olefin to thecracking zone. It has been found, however, regardless of how manyrecycles are employed, the ultimate yield or the ultimate decompositionof the olefin to the desired products at an appreciable yield per passis not greater than about 45 mol percent of the olefin being decomposed,the remaining 55 mol percent being converted to undesirable or unwantedproducts as a result of side reactions caused by the high temperature,the long residence time and the recycling steps employed. Thereby, afairly high percent of these products are, in a sense, wasted, in thatthe starting materials are converted to undesired products.

Therefore, this invention has as its main object a method whereby theoverall yield of the desired products produced by cracking on olefin maybe increased. Another object is to provide a method whereby the yieldper pass of desired products obtained when olefins are cracked may beincreased. Another object is to increase the ultimate yield or theultimate decomposition of olefins to the desired products. Still anotherobject is to provide a method whereby the residence time in the crackingzone of olefins may be decreased. Another object is to provide a methodwhereby olefins may be cracked at lower cracking temperatures. Anotherobject is to provide a method whereby the formation of undesiredproducts produced by side reactions during the cracking of olefins maybe decreased. Another object is to provide a method whereby the size ofthe equipment necessary to crack a given volume of an olefin is reduced.Another object is to reduce the amount of material required to berecycled. Still another object is to provide a method to promote thecracking of olefins to the desired products. Other objects will becomeapparent as the description proceeds.

In accordance with the present invention, olefins which contain in theirmolecules a carbon-to-carbon single bond in a position beta to thedouble bond are subjected to temperatures varying from about 400 C. toabout 900 C. for periods of time ranging from about 0.001 to about 3seconds, while said olefin is in the presence of at least one olefinpyrolysis initiator of the free radical type selected from the groupconsisting of acetaldehyde, dimethyl ether, ethylene oxide, methylethylether, propionaldehyde, acetone, methylethyl ketone, propylene oxide, inorder to cleave the carbon-to-carbon single bond in a position beta tothe double bond of said olefin.

Generally, the cracking of olefins in accordance with the practice ofthis invention may be carried out in any conventional manner usuallyemployed in the art of cracking olefins. Generally these conditionsemployed may be widely varied and are not critical. They usually dependupon the particular olefin to be cracked and the particular productswhich are desired. For instance, the cracking temperature may be variedwidely from about 400 C. to about 900 C. However, it is preferred topractice this invention at temperatures ranging between 500 and 800 C.and it is more preferable to employ temperatures ranging from about 600C. to about 750 C. The time that the olefins are in the cracking zoneduring the practice of this invention may range broadly from about 0.001to about 3 seconds. However, depending upon the particular olefincracked and the products desired, this time may vary from about 0.05 toabout 1 second and it is most preferred that this time range from about0.1 to about 0.5 second. These times are referred to usually asresidence time, that is residence time within the cracking zone and aredefined as the time required for 1 molecule of incoming gas, whether itbe reactant, diluent or both, to pass through the cracking Zone. Thecracking zone may be defined as the zone at which the temperature iselevated to the cracking temperatures as indicated above.

Generally, the olefins which are cracked in accordance with theinvention may be in pure form or in mixture with other hydrocarbons. Theolefins to be cracked may also be mixed with an inert diluent. It isusually desirable to employ an inert diluent when cracking olefins inaccordance with this invention. The term inert diluent is defined as amaterial which does not appreciably react or interfere with the olefinto be cracked. Likewise, the diluent does not react with the desiredproducts produced by the cracking at the cracking conditions employed orwith initiators employed in the cracking process. Furthermore, thisdiluent likewise should not crack or decompose itself at the conditionsemployed. Examples of diluents suitable for use in this invention aresteam, carbon dioxide, hydrogen, nitrogen, the inert gases such ashelium, neon and argon or parafiinic hydrocarbons such as methane,ethane, or various other hydrocarbons which themselves will not crack atthe temperatures employed in the cracking conditions of this invention.The ratio of diluent to olefin to be cracked which may be employed inthe practice of this invention, if any be employed, may widely vary fromabout 0.5/1 to about or more mols of diluent per mol of olefin. However,if more than about 15/1 ratio is employed, the improvement gained doesnot offset the cost accrued and the process could become uneconomical.Therefore, it is usually preferred to use a ratio of diluent to olefinof from about 1/1 to about 3/1 or 4/1 in this invention.

The pressure employed in the cracking zone is not critical and may varyfrom about 1 millimeter of mercury to about 500 pounds per square inchgauge. However, it is preferred to employ pressures ranging from about 1atmosphere to about 100 pounds per square inch gauge in the practice ofthis invention. Generally, it is preferred to employ oxygen-freeconditions when practicing this invention.

By the term olefin pyrolysis initiator of the free radical type as usedin this specification and claims is meant that the material generatesfree radicals when subjected to the operating conditions of thisinvention. In other words,

any material which at the operating conditions will decompose ordissociate to form a free radical will operate as an olefin pyrolysisinitiator. The preferred olefin pyrolysis initiators are acetaldehyde,dimethyl ether, ethylene oxide, methylethyl ether, propionaldehyde,acetone, methylethyl ketone, propylene oxide and the like. The amount ofolefin pyrolysis initiator which has been found useful in this inventionand which shows good improvement over thermal pyrolysis has been foundto vary broadly. (Since each mol of initiator generates one mol of freeradical, the amounts are best designated as mol percents.) It has beenfound that as little as 0.4 or 0.5 mol percent of initiator based on thetotal olefin is sufficient to cause an improvement. While there is noupper lllfllt to the amount of initiator which may be employed it hasusually been the practice to employ amounts Iupoto ab-otut mdol percent.However, very little imvemen 1S aine above warrant the eftra Cost. 50mol percent which would As was stated above, this invention is directedto methods of promoting or increasing the efficiency of cracking olefinswhich are subject to thermal cracking processes generally. Thus, olefinswhich, when subjected to the practice of this invention, will split atthe carbon'tocarbon single bond which is in the position beta to thedouble bond. It is most desirable to employ the process of this mventionwith those olefins which have a carbonto-carbon single bond in aposition beta to the double bond and which have the proper configurationso that when they decompose they result in products which predominantlyform diolefins.

Representative among the olefins havin a carbon single bond which is ina positio n be t d tz t lie double bond which will decompose to form asa major product, butadiene-l,3 when cracked in the presence of at leastone initiator of this invention. are hexenepentene-Z; cyclohexene;3-methyl butene-l; Z-heptene' methyl hexene-2; 2-octene; 5methylheptene-Z' 6-met hyl heptene-Z; and nonene-Z.

Representative among the olefins having a carbontocarbon single bondwhich is in a position beta to the double bond which will decompse toform, as a major product, Z-methyl butadiene-l,3 or isoprene whencracked in the presence of at least on initiator of this invention areZ-methyl pentene-2; S-methyl pentene-Z; Z-ethyl butene-l; 3,3-dimethylbutene-l; 2,3-dimethyl butene-l' 2 methyl hexene-Z; 3-methyl hexene-2;3,3-dimethyl pentene-l; Z-methyl heptene-2; 3-methyl heptene-2; 33-dimethyl hexene-l; 2,5-dimethyl hexene-Z; 3,5-dimdthylhexene-2;Z-methyl octene-Z; B-methyl octene-Z; 3 3-dimethyl heptene-l;2,5-dimethyl heptene-2; and 2 6-dimethyl heptene-2.

Representative among the olefins having a carbon-todouble bond, whichwill decompose to form, as a major product, 2-ethyl butadiene-l,3 whencracked in the presence of at least one initiator of this invention, are3-ethyl pentene-2; 2-ethyl pentene-Z; and 3-ethyl hexene-Z.

Representative among the olefins having a carbontocarbon single bondwhich is in a position beta to the double bond, which will decompose toform, as a ma or product, 2.3-dimethyl butadiene-1,3 when cracked in thepresence of at least one initiator of this invention, are 2,3-dimethylpentene-Z; 2,3,3-trimethyl butene-l; 2, 3,3-trimethyl pentene-l; and2,3-dimethyl heptene-Z.

Representative among the olefins having a carbon-tocarbon single bondwhich is in a position beta to the double bond, which will decompose toform, as a major product, 3-methyl pentadiene-1,3 when cracked in thepresence of at least one initiator of this invention, are 3-rnethylhexene-3; 3-methyl heptene-3; 3,4-dimethyl hexene-2; and 3,6-dimethylheptene-3.

Representative among the olefins having a carbon-tocarbon single bondwhich is in a position beta to the double bond, which will decompose toform, as a major product, 2-methyl pentadiene-1,3 and 4-methylpentadiene-l,3 when cracked in the presence of at least one initiator ofthis invention, are 2,4-dimethyl pentene s; Z-methyl heptene-3;4,4-dimethyl hexene-2; 2-propyl pentene-2', 2-methyl-3-ethyl pentene-l;and 2,6-dimethyl heptene-3.

Representative among the olefins having a carbontocarbon single bondwhich is in a position beta to the double bond, which will decompose toform, as

major products, the piperylenes, when cracked in the presence of atleast one initiator of this invention, are hexene-3; 4-methy1 pentene-Z;heptene-3; 4-methyl hexene-2; octene-3; 4-methyl heptene-Z; 6-methylheptene-3; 4,5- dimethyl heptene-Z; and 4,5,5-trimethyl hexene-2.

The practice of this invention is illustrated by the followingexperiments which are intended to be represent ative rather thanrestrictive of the scope of this invention.

All of the experiments were performed in a cracking assembly consistingof a hairpin" coil prepared from /4 inch OD. 316 stainless steel tubing.This cracking coil was immersed in a bed of fluidized heat transferpowder. This heat transfer powder was a microspheroidal alumina-silicamaterial normally employed as a cracking catalyst. This heat transferpowder was heated both by an electrical resistance heater and bycombusting a natural gas flame directly in the fluidized powder bed. Thetemperature gradient from the top to the bottom of the bed was nevermore than about 5 to 6 C. and the gradient from the fluidized bed to thecracking zone was never more than about 5 to 6 C. The temperatures weremeasured within the fluidized bed by means of conventional thermocoupletechniques. The cracking coil had conventional thermocopule wells andthe temperature within the cracking zone was also measured byconventional thermocouple techniques. The procedure employed was tobring the heat transfer powder up to about 500 C. by employing theelectrical resistance heaters, at the same time fluidizing the bed bymeans of air. Then a direct natural gas/air flame was employed to bringthe heat transfer bed up to the desired cracking or operatingtemperature. The natural gas flame and products of the combustion andadditional air was used to fluidize the powdered bed. The promoter orrefractory material was mixed with the olefin, which was to be cracked,in the desired mol percentage prior to the olefin being passed throughthe cracking zone. Water and the olefin containing the promoter, if any,were pumped at the proper rates necessary to produce the desired steamto hydrocarbon ratios and at an overall rate to give the desiredresidence time of the materials in the cracking zone. When all variableshad been adjusted to give the desired operating conditions, the productsof the cracking were collected; if liquid, by means of cooled receivers,and, if gas, they were metered at atmospheric pressure and roomtemperature conditions. The products collected were analyzed for contentand yields by conventional analytical methods. Conventional recycletechniques were employed to obtain the utlimate yields and are reportedas ultimate reaction efficiencies. pass yields are reported as the yieldper pass.

The results of each experiment as well as the operating conditions arereported in the table below wherein column 1 is the run number; column 2is the residence time in seconds; column 3 is the cracking temperaturein C.; column 4 lists the initiator employed, if any, and the amount inmol percent; column 5 is the yield of isoprene reported in mol per centper mol of olefin charged and IS the single pass yield and column 6 isthe ultimate yield and is reported as the mol percent of isopreneobtained per mol of olefin cracked while employing conventional recycletechniques.

In each of these examples products produced are isoprene and methane.All yields and efficiencies are based on the isoprene produced.

The per It can be seen from the results set forth in Table I that morethan a 30% greater yield of isoprene per pass is obtained by thepractice of this invention as opposed to true thermal decomposition of3-methyl-2-pentene.

Similar results may be obtained employing other olefins having in theirmolecule a carbon-to-carbon single bond in a position beta to the doublebond and other olefin pyrolysis initiators as well as other reactionconditions, all of which have been discussed elsewhere in thisapplication.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:

1. A cracking process which comprises providing a mixture of (a) atleast one olefin having in its molecule a carbon-to-carbon single bondin a position beta to the double bond and (b) at least one olefinpyrolysis initiator selected from the group consisting of acetaldehyde,dimethyl ether, ethylene oxide, methylethyl ether, and propionaldehyde,said pyrolysis initiator being present in said mixture in an amount ofat least 0.4 mol percent based on the olefin, subjecting said mixture totemperatures ranging from about 400 C. to about 900 C. for periods oftime ranging from about 0.001 to about 3 seconds. to cleave thecarbon-to-carbon single bond which is in a position beta to the doublebond of said olefin.

2. A cracking process which comprises providing a mixture of (a) atleast one olefin selected from the group consisting of 2-methylpentene-2; 3-methyl pentene-Z; 2-ethyl butene-l; 3,3-dimethyl butene-l;2,3-dimethyl-butene-1; 2-methyl hexene-Z; 3-methyl hexene-Z;3,3-dimethyl pentene-l; Z-methyl heptene-Z; 3-methyl heptene-Z;3,3-dimethyl hexene-l; 2,5-dimethyl hexene-2; 3,5-dimethyl hexene-2; and(b) at least one olefin pyrolysis initiator selected from the groupconsisting of acetaldehyde, dimethyl ether, ethylene oxide,methylethylether, and propionaldehyde, said pyrolysis initiator beingpresent in said mixture in an amount of at least 0.4 mol percent basedon the olefin, subjecting said mixture to temperatures ranging fromabout 400 C. to about 900 C. for periods of time ranging from about0.001 to about 3 seconds, to cleave the carbon-to-carbon single bondwhich is in a position beta to the double bond of said olefin, andthereby forming isoprene.

3. A cracking process which comprises providing a mixture of (a) atleast one olefin selected from the group consisting of 3-ethylpentene-Z; Z-ethyl pentene-2 and 3- ethyl hexene-2 and (b) at least oneolefin pyrolysis initator selected from the group consisting ofacetaldehyde. dimethyl ether, ethylene oxide, methylethyl ether, andpropionaldehyde, said pyrolysis initator being present in said mixturein an amount of at least 0.4 mol percent based on the olefin, subjectingsaid mixture to temperatures ranging from about 400 C. to about 900 C.for periods of time ranging from about 0.001 to about 3 seconds, tocleave the carbon-to-carbon single bond which is in a position beta tothe double bond of said olefin and thereby forming Z-ethylbutadiene-l,3.

4. A cracking process which comprises providing a mixture of (a) atleast one olefin selected from the group consisting of hexene-Z;3-methyl pentene-l; pentene-Z; cyclohexene; 3-methyl butene-l; Z-hepteneand S-methyl TABLE I [Pyrolysis ol' fl-Methyl-Q-Pontene to Isopreue]Exp. No. Residence Temp, C. Initiator and Amount, Isoprcno i ReactionTime, Sec. Mole Percent Yield, Mole Etllc., Percent Percent l l n 0.15668.5 Nonezusnns." CV... 15.6 61.2 2 0. 15 673. 0 Acetaldchytle, 10%2t). 4 61. l

hexene-Z and (b) at least one olefin pyrolysis initiator selected fromthe group consisting of acetaldehyde, dimethyl ether, ethylene oxide,methylethyl ether, and propionaldehyde, said pyrolysis initiator beingpresent in said mixture in an amount of at least 0.4 mol percent basedon the olefin. subjecting said mixture to temperatures ranging fromabout 400 C. to about 900 C. for periods of time ranging from about0.001 to about 3 seconds, to cleave the carbon-to-carbon single bondwhich is in a position beta to the double bond of said olefin andthereby forming butadiene-1,3.

5. A cracking process which comprises providing a mixture of (a) atleast one olefin selected from the group consisting of hexene-3;4-methyl pentene-Z; heptene-3; 4- methyl heXene-2; octene-3; 4-methylheptene-Z and 6- methyl heptene-3 and (b) at least one olefin pyrolysisinitiator selected from the group consisting of acetaldehyde, dimethylether, ethylene oxide, methylethyl ether, and propionaldehyde, saidpyrolysis initiator being present in said mixture in an amount of atleast 0.4 mol percent based on the olefin, subjecting said mixture totemperatures ranging from about 400 C. to about 900 C. for periods oftime ranging from about 0.001 to about 3 seconds, to cleave thecarbon-to-carbon single bond which is in a position beta to the doublebond of said olefin and thereby forming piperylene.

6. A process according to claim 1 in which the olefin pyrolysisinitiator is acetaldehyde.

7. A process according to claim 1 in which the olefin pyrolysisinitiator is ethylene oxide.

8. A process according to claim 2 in which the olefin is Z-methylpentene-2.

9 A process according to claim 2 in which the olefin is 3-methylpentene-Z.

10. The method according to claim 3 in which the olefin is 3-ethylpentene-2.

11. The method according to claim 4 in which the olefin is peritene-2.

12. The method according to claim 5 in which the olefin is heXene-3.

13. The method according to claim 5 in which the olefin is 4-methylpentene-2.

14. The method according to claim 8 in which the olefin pyrolysisinitiator is acetaldehyde.

15. The method according to claim 9 in which the olefin pyrolysisinitiator is acetaldehyde.

16. The method according to claim 8 in which the olefin pyrolysisinitator is ethylene oxide.

17. The method according to claim 10 in which the olefin pyrolysisinitiator is acetaldehyde.

18. The method according to claim 11 in which the olefin pyrolysisinitiator is acetaldehyde.

19. The method according to claim 12 in which the olefin pyrolysisinitiator is acetaldehyde.

20. The method according to claim 13 in which the olefin pyrolysisinitiator is acetaldehyde.

References Cited by the Examiner UNITED STATES PATENTS 2,259,630 10/1941Frey et al. 260683 3,209,048 9/1965 Burk et a1 260-680 3,211,737 10/1965Burk et al 260-680 3,238,270 3/1966 Turnquest 260-680 3,254,136 5/1966Frech 260-680 DELBERT E. GANTZ, Primary Examiner.

G. E. SCHMITKONS, Assistant Examiner.

